Signal of the LIGO-like interferometer with perpendicular arms of length \(L\) 
along the direction of unit vectors \(\hat{a}\)  and \(\hat{b}\)  is proportional
to the relative phase shift \(\Delta \varphi \)  of electromagnetic waves
traveling a roundtrip distance \(2L\)  along the two arms [1]}
\(\Delta \varphi =\frac{2\omega L}{c}\left[ (\hat{a}\cdot \hat{k})(\hat{a}\cdot \mathbf {h})-(\hat{b}\cdot \hat{k})(\hat{b}\cdot \mathbf {h})\right] ,\) 
